The present invention relates to an electronically controlled mechanical timepiece for accurately driving hands fixed to a train wheel by converting the mechanical energy of a mechanical energy source, such as a mainspring, into electrical energy by a generator and controlling the rotational cycle of the generator by actuating a rotation controller powered by the electric energy.
Japanese Examined Patent Publication No. 7-119812 and Japanese Unexamined Patent Publication No. 8-101284 disclose electronically controlled mechanical timepieces for displaying time by driving hands fixed to a train wheel by converting mechanical energy generated by the release of a mainspring into electrical energy by a generator and controlling the value of the current flowing to the coil of the generator by actuating a rotation controller by the electrical energy.
In the timepieces of the above references, it is important to increase braking torque when the mainspring has high torque and prevent a drop of generated power at the same time to increase the time with which the timepiece may be powered by the electrical energy. For this purpose, the electronically controlled mechanical timepiece disclosed in Japanese Examined Patent Publication No. 7-119812 provides an angular range where the rotating velocity of a rotor is increased by turning off a brake to increase the amount of generated power each time the rotor rotates. That is, a brake is released during each rotation of the rotor to permit more power to be generated to compensate for the drop in generated power when the brake is applied over an angular range.
Further, the timepiece disclosed in Japanese Unexamined Patent Publication No. 8-101284 increases braking torque and prevents a drop of a generated voltage at the same time by boosting the voltage of the power induced by a generator with a number of stages of a boosting circuit.
However, in the timepiece disclosed in Japanese Examined Patent Publication No. 7-119812, the rotor is switched from a state in which it rotates at a high rotating velocity to a state in which it rotates at a low rotating velocity. The abrupt velocity change is difficult to realize as the rotor almost stops during each rotation. In particular, because a fly wheel is typically provided to increase the rotational stability of the rotor, it is difficult to abruptly change the velocity of the rotor.
Further, since generated power is reduced when the brake is applied, a limit is reached in suppressing the reduction in the loss of generated power while increasing braking torque.
On the other hand, because the electronically controlled mechanical timepiece disclosed in Japanese Unexamined Patent Publication No. 8-101284 requires a number of switches and capacitors, the cost of the design is increased.
Accordingly, it is desirable to provide a timepiece that overcomes the drawbacks of the prior art.
Generally speaking, in accordance with the invention, an electronically-controlled, mechanical timepiece preferably can include a mechanical energy source, a generator driven by the mechanical energy source coupled therewith through a train wheel. The generator generating induced power and supplying electrical energy from first and second terminals of the generator, and hands coupled with the train wheel. A rotation controller, driven by the electric energy can be provided to control the rotational cycle of the generator, and can include a switch for short-circuiting the respective terminals of the generator, and wherein the rotation controller uses chopping to control the generator by intermittently actuating the switch.
The electronically controlled mechanical timepiece of the present invention drives the hands and the generator by a mainspring and regulates the number of rotations of a rotor (and thereby the rotation of the hands) by applying a brake to the generator by the rotation controller. The generator rotation is controlled by chopping the generator by activating and deactivating the switch that short circuits the ends of the generator coil. When the switch is activated, a short-circuit brake is applied to the generator by chopping and energy is stored in the coil of the generator. Whereas, when the switch is deactivated, the generator is operated and a voltage generated thereby is increased by the energy stored in the coil. As a result, when the generator is controlled by chopping, a loss of generated power caused when the brake is applied can be compensated by an increase in the generated voltage when the switch is deactivated. Thus, brake torque can be increased while keeping the generated power to at least a prescribed level so that the timepiece can have a long life.
Since the effect of increasing the generated voltage is diminished when the chopping frequency is lower than five times the waveform frequency of the generated voltage, it is preferable that a chopping frequency for intermittently activating the switch by the rotation controller is at least five times as large as the waveform frequency of the voltage generated by the rotor of the generator at a set velocity. It is more preferable that the chopping frequency is five to one hundred times as large as the waveform frequency of the voltage generated by the rotor of the generator at the set velocity.
When the chopping frequency is more than one hundred times as large as the waveform frequency of the generated voltage, an IC for executing chopping consumes a large amount of power. Thus, it is preferable that the chopping frequency is one hundred times or less the waveform frequency of the generated voltage. Further, because the changing ratio of torque to the changing ratio of a duty cycle approaches a prescribed level when the chopping frequency is five times to one hundred times as large as the waveform of the generated voltage, the control can be easily carried out. However, the chopping frequency may be set to less than five times or greater than one hundred times the value of the generated voltage waveform depending upon the use and the control method.
In a preferred embodiment, the timepiece includes first and second power supply lines for charging the electrical energy of the generator to a power supply circuit, wherein the switch is composed of a first and a second switch, preferably transistors, interposed between the first and second terminals of the generator and one of the first and second power supply lines, respectively, and the rotation controller continuously activates the switch connected to one of the first and second terminals of the generator as well as intermittently activates the switch connected to the other terminal of the generator.
With this arrangement, since the control of the power generating process and the rotation process of the generator can be simultaneously carried out in addition to the brake control by chopping, cost can be reduced by decreasing the number of parts as well as an improvement can be attained in power-generating efficiency by controlling the timing at which the respective switches are activated.
Further, it is preferable that the rotation controller includes comparators for comparing the waveforms of the voltage generated by the generator with a reference waveform, a comparison circuit for comparing the output from each comparator with a time standard signal and outputting a difference signal, a signal output circuit for outputting a pulse-width varied clock signal based on the difference signal, and a logic circuit for ANDing the clock signal and the output from each comparator and outputting an ANDed signal to the transistors.
With this arrangement, because the power consumed to intermittently control the transistors can be reduced, a circuit may be arranged that is suitable for the generator of a clock that generates a small amount of power.
A preferred embodiment of the timepiece includes a first switch that includes a first field effect transistor having a gate connected to the second terminal of the generator and a second field effect transistor connected in series to the first field effect transistor is intermittently activated by the rotation controller. The second switch includes a third field effect transistor having a gate connected to the first terminal of the generator, and a fourth field effect transistor connected in series to the third field effect transistor that is intermittently activated by the rotation controller. Further, one of the first and second diodes are interposed between one of the first and second terminals of the generator and one of the first and second power supply lines, respectively.
In another preferred embodiment, the first switch is preferably composed of a first field effect transistor having a gate connected to the second terminal of the generator that is a second field effect transistor connected in series to the first field effect transistor and intermittently activated by the rotation controller. The second switch is preferably composed of a third field effect transistor having a gate connected to the first terminal of the generator and a fourth field effect transistor connected in series to the third field effect transistor that is intermittently activated by the rotation controller. A boost capacitor is interposed between one of the first and second terminals of the generator and the other of the first and second power supply lines and a diode is interposed between the other of the first and second terminals and the other of the first and second power supply lines.
In the timepiece constructed as described above, when the first terminal of the generator is positive and the second terminal thereof is negative (i.e., the second terminal has lower potential than that of the first terminal), the first field effect transistor, whose gate is connected to the second terminal, is activated, and the third field effect transistor, whose gate is connected to the first terminal, is deactivated. As a result, the a.c. current generated by the generator flows through the path composed of the first terminal, the first field effect transistor, one of the first and second power supply lines, the power supply circuit, the other of the first and second power supply lines and the second terminal.
When the second terminal of the generator is set to positive and the first terminal thereof is set to negative (i.e., the first terminal has a lower potential than that of the second terminal), the third field effect transistor whose gate is connected to the first terminal, is activated, and the first field effect transistor, whose gate is connected to the second terminal, is deactivated. As a result, the a.c. current generated by the generator flows through the path composed of the second terminal, the third field effect transistor, one of the first and second power supply lines, the power supply circuit, the other of the first and second power supply lines and the first terminal.
At that time, the second and fourth field effect transistors are repeatedly activated and deactivated in response to the chopping signals input to their gates. Since the second and fourth field effect transistors are connected in series to the first and third field effect transistors, when the first and third field effect transistors are activated, a current flows regardless of the activation state of the second and fourth field effect transistors. However, when the first and third field effect transistors are deactivated, current flows when the second and fourth field effect transistors are activated in response to the chopper signal. Therefore, when the second and fourth field effect transistors, which are connected in series to one of the first and third field effect transistors in the deactivated state, are activated in response to the chopping signal, both the first and second switches are activated to thereby short-circuit the respective terminals of the generator.
With this operation, the generator may be subjected to a brake control by chopping so that a drop of generated power when the brake is applied can be compensated by an increase in the generated voltage when the switch is deactivated. In this way, brake torque can be increased, while maintaining generated power to at least a prescribed level so that the life of the timepiece is prolonged. Further, since the generator is rectified by the first and third field effect transistors whose gates are connected to the respective terminals, a comparator and the like are not required, thereby simplifying the construction as well as preventing a drop in the charging efficiency due to the power consumed by the comparator. Further, since the field effect transistors are activated and deactivated making use of the terminal voltage of the generator, the respective field effect transistors can be synchronized with the polarities of the terminals of the generator, thereby improving the rectifying efficiency.
When a boost capacitor is interposed between one of the terminals of the generator and a power supply line as described above, the power supply circuit and the boost capacitor can be simultaneously charged when the terminal voltage of the terminal to which the capacitor is connected is increased. Whereas, when the voltage of the other terminal of the generator is increased, the power supply circuit can be charged with a high voltage obtained by adding the voltage charged to the boost capacitor to the voltage induced by the generator.
The rotation controller can include a chopper signal generator for generating at least two types of chopper signals having different duty ratios and at least the two types of chopper signals can be imposed on the switch to thereby perform chopping control of the generator.
In the present invention, when the switch for short-circuiting both terminals of the generator is provided and the generator is controlled by imposing the chopping signal to the switch, although a lower chopper frequency and a higher duty ratio can provide increased drive torque (brake torque) and the higher chopper frequency increases the charged voltage (generated voltage), the drive torque and voltage generated are not significantly reduced even if the duty ratio is increased. This effect is found where the charged voltage is increased until the duty ratio is about 0.8 when the chopper frequency is at least 50 Hz. Thus, the generator can be controlled by chopping using at least the two chopper signals having different duty ratios.
It is preferable that the rotation controller includes a brake controller for detecting the rotational cycle of the generator and applying a brake to the generator based on the rotational cycle and a brake deactivation control for releasing the brake. The brake controller imposes chopper signals having different duty ratios on the switch in the brake-activation control and the brake-deactivation control. For example, preferably, the chopper signal imposed in the brake-activation control can have a duty ratio larger than that of the chopper signal imposed in the brake-deactivation control.
The timepiece of the present invention can drive the hands and the generator by a mainspring and regulate the number of revolutions of the rotor (and hence the hands) by applying a brake, controlled by a rotation controller, to the generator.
The rotation control of the generator is carried out by imposing a chopper signal on the switch capable of short-circuiting both ends of the generator coil and turning the switch on and off, that is, by chopping the switch. When the switch is activated by the chopping, a short-circuit brake is applied to the generator and energy is stored to the generator coil. Whereas, when the switch is deactivated, the generator is operated and a voltage generated thereby is increased by the energy stored in the coil. As a result, when the generator is controlled by the chopping in the application of the brake, a drop of the generated power caused when the brake is applied can be compensated by an increase of the generated voltage when the switch is deactivated. In this manner, brake torque (brake torque) can be increased while preventing a drop in the generated power so that the timepiece life is prolonged.
When the brake activation control in which the brake is applied by imposing at least two types of chopper signals having different duty ratios on the switch, the control torque of the generator can be increased and a drop of the generated power can be prevented by using a chopper signal having a large duty ratio (during which the switch is activated for a longer period than the switch is deactivated).
On the other hand, when the brake is released, the brake torque of the generator can be greatly reduced and the generated power can be sufficiently maintained by using a chopper signal having a duty ratio smaller than that of the chopper signal described above.
The application of the brake by a chopper signal having a large duty ratio and the release thereof by means of the chopper signal having a small duty ratio permits an increase of the brake torque while suppressing a drop of the generated power (power charged to a capacitor and the like), whereby an electronically controlled mechanical timepiece having a long life can be arranged.
Although the brake-activation control and the brake-deactivation control are ordinarily carried out once in each reference cycle of the generator (for example, the cycle during which the rotor rotates once), in one embodiment, only the brake-deactivation control may be carried out during a plurality of the reference cycles just after the generator is started.
Further, although the duty ratio of the respective chopper signals may be set in accordance with the characteristics of the generator to be controlled, a chopper signal having a large duty ratio of, for example, about 0.7 to 0.95, and a chopper signal having a small duty ratio of about, for example, 0.1 to 0.3 can be used.
In another embodiment, the rotation controller includes a chopper signal generator for generating a chopper signal and brake controller for switching a brake-activation control for detecting the rotational cycle of the generator and applying a brake to the generator based on the rotational cycle and a brake-deactivation control for releasing the brake. In this embodiment, the brake controller imposes the chopper signal on the switch only in the brake-activation control to thereby perform chopping control of the generator.
Since the chopping signal is imposed only in the brake activation control which, in this case, also needs to control a brake, the brake torque of the generator can be increased and a drop of generated power can be suppressed by chopping.
The rotation controller can include a chopper signal generator for generating at least two types of chopper signals having a different frequency, which are imposed on the switch to thereby chopping control the generator.
It is preferable that the rotation controller includes a brake controller for switching a brake activation control for detecting the rotational cycle of the generator and applying a brake to the generator based on the rotational cycle and a brake deactivation control for releasing the brake, wherein the brake controller uses chopper signals having different frequencies on the switch in the brake activation control and the brake deactivation control and the chopper signal imposed in the brake activation control has a frequency smaller than that of the chopper signal imposed in the brake deactivation control. When the chopper signal imposed on the switch has a high frequency, the drive torque (brake torque) is reduced so that a braking effect is decreased and the charged voltage (generated voltage) is increased. On the other hand, when the chopper signal having a low frequency is imposed, the drive torque is increased, the braking effect is increased, and the charged voltage is reduced as compared with the case where the frequency is high. However, since chopping is carried out, the charged voltage is increased as compared with a case where only a brake control is executed.
Therefore, where the brake is applied during brake activation control, the brake torque of the generator can be increased by using a chopper signal having a low frequency while suppressing a drop of the generated power by the chopping. On the other hand, where the brake is released during brake-deactivation control, the brake torque of the generator can be greatly reduced by using a chopper signal having a frequency which is higher than that used during brake activation control, thereby generating sufficient power.
The brake torque can be increased while suppressing a drop of the generated power by applying the brake using a chopper signal having the low frequency and releasing the brake using a chopper signal having the high frequency, whereby an electronically controlled mechanical timepiece having a long life can be arranged.
Although the frequency of the respective chopper signals may be set in accordance with the characteristics of the generator to be controlled, a chopper signal having a high frequency of, for example, about 500-1000 Hz and a chopper signal having a low frequency of, for example, about 10-100 Hz can be used.
Further, the chopping control may be carried out using chopper signals having not only a different frequency but also a different duty ratio. In particular, brake control can be effectively carried out when a chopper signal having a low frequency and a high duty ratio is used in the brake activation control and a chopper signal having a high frequency and a low duty ratio is used in the brake deactivation control.
The rotation controller can include a chopper signal generator for generating at least two types of chopper signals having different frequencies and a voltage sensor for detecting the voltage of a power supply charged by the generator. Where the voltage of the power supply detected by the voltage sensor is lower than a set value, a chopper signal having a first frequency can be imposed on the switch, and when the detected voltage of the power supply is higher than the set value, a chopper signal having a second frequency, which is lower than the first frequency, can be imposed on the switch.
In one embodiment, the rotation controller preferably includes a brake controller for switching a brake activation control, for detecting the rotational cycle of the generator, and for applying a brake to the generator based on the rotational cycle, and a brake deactivation control for releasing the brake. The chopper signal generator can generate two types of chopper signals having a different duty ratio at first and second frequencies. The brake controller can use chopper signals having one of a first and second frequencies selected in correspondence to the power supply voltage and a different duty ratio than the switch in the brake activation control and the brake deactivation control, respectively.
In the present invention arranged as described above, the chopper signal for executing the brake control of the generator is switched to a chopper signal having a different frequency in accordance with the power supply voltage (for example, the voltage charged to the capacitor by the generator). Accordingly, when the power supply voltage is lower than a predetermined value, a chopper signal can be used that decreases brake torque and increases charged voltage (that is, which gives priority to charging rather than a braking effect), whereas when the power supply voltage is higher than the predetermined value, a chopper signal can be used that increases the brake torque and decreases charged voltage (that is, which gives priority to the brake rather than a charging effect), so that a proper brake control can be carried out in accordance with a charged state.
Further, it is preferable that the rotation controller synchronizes the time at which the brake activation control for applying the brake to the generator and the brake deactivation control for releasing the brake are switched with a time when the switch is intermittently activated in response to the chopper signal. When the timing of the brake is synchronized with the timing of the chopping signal, the chopper signal can also be used as a pace measuring pulse.
In a further embodiment, the rotation controller can include a rotational cycle sensing for detecting the rotational cycle of the rotor by means of a rotor rotation sensing signal, which is set to one of a low-level signal and a high-level signal when the voltage of the rotational waveform of the generator is compared with a reference voltage at a time of chopping and the voltage of the rotational waveform is equal to or lower than the reference voltage, and to the other of the low-level signal and the high-level signal when the voltage of the rotational waveform is higher than the reference voltage.
It is preferable that the rotation controller sets the rotor rotation sensing signal to one of the low-level signal and the high-level signal when the voltage of the rotational waveform of the generator is compared with the reference voltage at the time of chopping and is continuously equal to or lower than the reference voltage n number of times, and sets the rotor rotation sensing signal to the other of the low-level signal and the high-level signal when the voltage of the rotational waveform of the generator which is compared with the reference voltage at the time of chopping is continuously higher than the reference voltage m number of times. In addition, it is preferable that n and m are based on a chopping frequency and a noise frequency superimposed on the rotational waveform of the rotor.
When the generator is controlled by chopping, a chopper pulse is superimposed on the rotational waveform of the rotor of the generator. Therefore, the voltage of the rotational waveform of the rotor is compared with the reference voltage at the time the chopper pulse is superimposed (i.e., time at which the chopping is executed) to obtain a rectangular wave signal (rotor rotation sensing signal) that corresponds to the rotational cycle of the rotor from the rotational waveform of the rotor.
At that time, noise such as an external magnetic field (for example, a commercial power supply having a frequency of 50/60 Hz) may be superimposed on the rotational waveform of the rotor and there may arise such a case that the rotational waveform of the rotor is deformed by the effect of the noise and the rotor rotation sensing signal cannot be correctly obtained. To cope with this problem, whether the rotational waveform of the rotor is equal to or less than the reference voltage or greater than the reference voltage can be correctly and reliably detected so that the erroneous detection of the rotor rotation sensing signal caused by the effect of the noise can be prevented by setting the rotor rotation sensing signal to one of the low-level signal and the high-level signal when the voltage of the rotational waveform of the generator is continuously equal to or lower than the reference voltage n number of times, and setting the rotor rotation sensing signal to the other of the low-level signal and the high-level signal when the voltage of the rotational waveform of the generator (which is compared with the reference voltage at the time of chopping) is continuously higher than the reference voltage m number of times.
Further, the rotation controller may set the rotor rotation sensing signal to one of the low-level signal and the high-level signal when the voltage of the rotational waveform of the generator (which is compared with the reference voltage at the time of chopping) is continuously equal to or lower than the reference voltage x number of times and set the rotor rotation sensing signal to the other of the low-level signal and the high-level signal when the rotational waveform of the generator (which is compared with the reference voltage at the time of chopping) is higher than the reference voltage y number of times (which may not be continuous). It is preferable here that the x times and the y times are set based on a chopping frequency and a noise frequency superimposed on the rotational waveform of the rotor.
Whether the rotational waveform of the rotor is equal to or less than the reference voltage or greater than the reference signal can be correctly and reliably detected and the erroneous detection of the rotor rotation sensing signal caused by the effect of the noise can be prevented.
Further, the rotation controller may control the rotation of the rotor using a PL control and may control the rotation of the rotor using an up/down counter. In short, the rotation controller may control the rotation of the rotor using any means so long as it compares the rotational waveform of the rotor with the reference waveform from a quartz oscillator and carries out the brake control of the generator so as to reduce the difference therebetween.
A method of controlling an electronically controlled, mechanical timepiece of the present invention is provided that includes the steps of comparing a reference signal based on a signal from a time standard source with a rotation sensing signal output that corresponds to the rotational cycle of the generator, intermittently activating a switch capable of short-circuiting the respective terminals of the generator in accordance with an amount of advance of the rotation sensing signal with respect to the reference signal and subjecting the generator to a brake control by chopping.
According to the above control method, because the rotation control (brake control) of the generator is carried out by chopping the activation and deactivation of the switch capable of short-circuiting both the ends of the generator coil, a drop in generated power caused when the brake is applied can be compensated by an increase of the generated voltage when the switch is deactivated. In this way, control torque can be increased while keeping the generated power to at least a prescribed level so that the life of an electronically controlled mechanical timepiece can be prolonged.
A second method of controlling an electronically controlled mechanical timepiece is provided, and includes the steps of inputting a reference signal based on a signal from a time standard source and a rotation sensing signal output that corresponds to the rotational cycle of the generator to an up/down counter by setting one of the signal as an up-count signal and the other of the signals as a down-count signal, applying a brake to the generator by chopping when the counter value of the up/down counter is a predetermined value and not applying the brake to the generator when the counter value is a value other than the predetermined value.
According to the above control method, when the counter value of the up/down counter is the predetermined value (that is, when the torque of the mechanical energy source, such as a mainspring, is increased and the rotation of the generator is increased), a brake is continuously applied by chopping until the difference between the respective count values disappears. As a result, brake torque can be increased while keeping generated power to at least a prescribed level, whereby a rotational velocity can be promptly and correctly regulated so that a control can be executed with excellent responsiveness. Further, since counting and the comparison of respective count values can be performed at the same time by the up/down counter, the construction can be simplified and the difference between the respective count values can be simply determined.
As described above, according to the electronically controlled mechanical timepiece of the present invention, torque for controlling the generator can be increased while keeping generated power to at least a prescribed amount as well as a cost can be also reduced.
An object of the present invention is to provide an electronically controlled mechanical timepiece capable of increasing the braking torque of a generator while keeping generated power at least at a prescribed level, and reduce the cost of the timepiece construction.
Other features of the present invention will become apparent from the following detailed description, considered in conjunction with the accompanying drawing figures. It is to be understood, however, that the drawings, which are not to scale, are designed solely for the purpose of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims.